Pleurobranchaea californica has hundreds of giant neurons (>200-500 [unreadable]M) which are identified as putative NOS-containing neurons in the central nervous system. A very high level of NO production (2-30 [unreadable]M) from the CNS has been directly demonstrated both in vitro and also in tissue homogenates. Nitric oxide production was shown to be L-arginine and NADPH dependent and could be inhibited by NOS inhibitor, 7-nitroimidazole. However, many other NOS inhibitors (known to be effective inhibitors for vertebrate tissues or cells such as L-NAME, L-NMMA and L-NA) were observed to enhance NO production in molluscan nervous tissue homogenates. The exact mechanisms of this unusual phenomenon are currently under investigation.